I have been busy working on giving Bernie a way to get around. He won't be autonomous (that's a whole other level of complexity and honestly I don't need a dragon who can move around when I'm not there, that's just going to lead to disaster!), but he will be able to move around on wheels under control from the Playstation controller and he has four legs to crawl around on.

Each leg has a bearing joint in the knee/elbow, which is made up of a screw, nut, some washers and most importantly one rivet attached to each piece of wood to allow the parts of the leg to move around the screw without too much friction.

Once in place, the bearings work very nicely for letting the leg move, but they initially didn't do much to stop the leg splaying out to the side, so to avoid this I added the third rivet which you can see in the top picture, as well as a second section of the lower leg which is supported by a 6mm spacer (just visible in the picture on the left) to allow the joint to move freely around the screw without moving sideways. I also replaced the nuts with nyloc nuts so that the repeated rotation and vibration doesn't continually loosen the joint. This way tightening the nut on each joint gives me very good control over how much resistance the joint offers to rotation as well as how much the lower leg wobbles around.

Reconnecting the legs to the body and wiring up the servos to the arduino made it very simple to test out a basic walking motion. The timing still needs some work, and without the wheels and tail to provide resistance the whole body has a tendency to wobble around, but the basic idea is there and the pulley system seems to be working nicely.

To make the legs move a bit nicer I need to make the hips more rigid by adding some blocks around the join to the spine and also reinforce the screws joining the servo horns to the hips. hopefully I will have that done by the end of the week and can move on to the final programming of the walk motion.

Did you notice he's not actually getting anywhere? I have some lovely little micro geared motors and wheels from pololu (bought through littlebirdelectronics) which I have wired up through an ardumotor shield and will be mounting as soon as possible, however the scroll saw is out of action for the moment so I can't cut the recesses in the body to mount the axle supports. These will also raise the body off the floor by about 15mm so the legs can move more easily without rocking the body from side to side.

I trialed the position of the servos with clamps, then used some right angle brackets from active-robots and some very useful plastic rivets to mount the servos onto the hips and shoulders.

He's not quite back together yet, but Bernie now has legs which is a big change and his balance has improved a lot already. The same pulley mechanism I designed on cardboard is done here with some brass hooks on the back of the legs.

I can't test this just yet though, because as you can see in the picture on the right all of the electronics are not currently inside Bernie. Since access is going to be tricky once the wing plate is attached I want to get as much tidied up as I can before his stomach gets any harder to access than it needs to be (the spare rib will still give me access when I need it, but it's going to be a bit of a squeeze to do anything in there).

Bernie woke up to a very bad morning. In order to add on legs there were a few modifications needed, so it was time to finally pull him apart completely.

While he was in pieces I took the opportunity to create a flat section on his back to support the wings he hopes to have eventually. This means he is going to have a metal plate inserted along his spine to carry the extra load, and also to make the body more rigid. Unfortunately once this is in place there will be a lot less access to the internal electronics, so I need to do as much as I can before I do that.

It's been quite a long time since I've updated here, which sadly reflects just how long it has been since I've had some spare time to work on Bernie: between organizing the Melbourne Mini and studying for exams it's been a very busy couple of months! I finally have some holidays so I can get going on Bernie and flesh out some of the designs I've been working on.

Poor Bernie has been sitting there on the coffee table unable to move for a while now. He has developed a bit of a lean because his poor tummy is carrying all of his weight, He can't even wave when people come to visit him. Clearly this must be fixed, and as many a quadruped knows, limbs are handy things to have around.

I've been thinking about how to do this for a while now, because I want to use just one servo motor to control the whole limb. This will reduce the load on the arduino, simplify the programming and make the leg lighter, but makes the mechanism more complicated to design. I started by playing with some cardboard, and then went back to the drawing board to see how I could make this idea work. Like all of this project, there is a lot of documentation which will probably never see the light of day, but it sure does help fill a boring lecture and makes construction much easier and quicker.

Just like my very first bit of body construction I decided to make a cardboard prototype to see if my idea really worked. Initially I had different designs for the arms and legs because they are such different shapes, but I didn't like the extra complexity in the legs so I have decided to modify the design to work on a single concept. The joints work because the string does not change length - both ends are fixed to the leg, but there is a pulley point on the body so that the relative motion of the leg to the body makes the elbow/knee extend.

Before anyone asks, these legs are not in any way load rated! They will not be carrying the weight of the dragon, just providing some balance and making him look less like a glorified snake.

The last two days have been great, so many packages arriving all at once!

From little bird electronics I got the second servo for the tail so that they would be matched. This is now installed but not yet plugged in or configured (although I have written the code already, so hopefully it works!)

More importantly, part of my order from DFRobot included a pan and tilt kit, which I have constructed and installed. Bernie can now look around - up and down as well as left and right. To do this though I had to CUT OFF HIS HEAD! Normally it is measure twice cut once, but I think this time I may have measured about 20 times. That cut would be hard to undo!

The neck now looks very mechanical, but moves very smoothly and can do so many things, I look forward to playing around with it. I will upload new video once I have it automated.

I have reached my target of having a moving tail before uni starts, and with a week to spare so now I have to decide what to do next!

dragon's spine with *new* tail

After talking about it with dad, I decided that rather than using a chain of seperate servos to move the tail, I could use just one at the base of the tail to move the whole thing. To make it curve I needed a more flexible material than MDF. In order to make it possible to change between the existing MDF spine and the new material, I decided that it would be great if the new material could also be 6mm thick. To get the flexibility at this thickness I chose to use strip rubber, which is very flexible but has enough strength at 6mm to avoid collapsing on itself. This did mean cutting the tail off the dragon, but replacing it was very easy with a couple of joining plates and bolts.

The tail is manipulated by a string attached to the servo, which passes through a series of hooks before reaching the tip of the tail. So far the tail can only wave one way - I have to buy another servo to manipulate the tail in the opposite direction, but it will operate in exactly the same way.

The base of the tail tends to get stuck on the table - it works better on a flat surface, but I will still need to smooth the bottom of the rubber as it has far too much friction and bends towards the table too much.

Tonight I cut the pieces out of an A3 copy of the skeleton drawings and traced them onto 3mm MDF in preparation for cutting them later this week. The Dragon consists of 24 seperate pieces which will have to be individually cut. The spine is not on this board, because it is going to be cut from a piece of 6mm MDF to give it extra strength. The pieces are laid out in strips so that the wood can be rough cut using a table saw in order to make it easier to handle.

Each of the ribs and other symmetrical parts were cut from paper, folded in half and marked to indicate the center to both ensure that the parts are even on both sides and also to help allign the slots which will be cut into the parts to allow them to slot together.

The actual layout is slightly different because I decided not to place pieces within the ribs to make it easier to cut.

I finished the initial skeleton design work and rather impatiently wanted to see if the concept worked the way I was picturing it. To test it out I scanned the pages of the design and printed them onto A4 card. Overall I am pretty happy with how the design works - I was especially excited to have the shoulders and hips fit together and sit flat along the ground!

I have already discovered that one of the most difficult parts of the dragon to get looking right is the head, and I have had particular trouble with the horns and nose regions. These are the only parts I have had to alter from the inital design (so far), and I expect that making the face look right will be an ongoing difficulty.

The horns I started with had a wavy edge shape, which looked ok in theory but once I cut them out it looked like the dragon was wearing lollies on his head! The new horns are double arc shapes which look much more menacing.

The jaw is designed to hinge from the skull, and is only attached by a split pin at the moment. When constructed from wood it will be made by two parallel sections connected at the tip and pivoting around a point on the base of the skull. In order to make it more realistically shaped, I may need to add in additional ribbing on the lower jaw.

After a couple of days of planning how to construct him I spent a fair bit of today designing what he will look like. So far, I have a sketch of the overall shape, and I have started to draw the templates for cutting out the body frame (skeleton). In fact, I got so into drawing that it is after midnight and I only have the tail section to go - that will have to wait until tomorrow!